The present invention relates to an apparatus and method for demonstrating the liquid level in a translucent storage tank, and specifically to very large tanks used in commercial industry.
Use of large volumes of water or other liquid chemicals is common in many industrial applications, including pharmaceutical, chemical production, and the semiconductor industry. In silicon wafer manufacturing, for example, it is common to use one million gallons of water or more each day. In these industries, it is very important to use very clean water, and therefore requires the use of reverse osmosis, deionization, or other purification techniques to prepare incoming water for manufacturing use. After the water has received one or more purification processes, the water is stored in very large tanks until its use is required. These tanks are typically made of fiber reinforced plastic, and are somewhat translucent. The tanks cannot be transparent, however, as biological growth would be induced.
With water consumption, there is considerable fluctuation in the volume of liquid in the tank at any given time. Typically, the liquid level of the tank is measured by a pressure transducer, and conveyed to an attached indicator. The percentage of liquid in the tank, or alternatively the inches of liquid in the tank, is shown on a dial indicator gauge, with calibration of the pressure transducer and indicator required on a periodic basis.
Liquid level alarms are tied into facilities management systems or process controllers to warn the facilities operator of a high level or low level condition. However, with such high water consumption, there is naturally a high flow through the tanks supply and discharge ports. This can result in the operator having very little time to respond to a high level or low level condition. In the absence of an alarm being activated, the operator must go to the dial indicator gauge to determine the fluid level in the tank. When multiple tanks are used, this compounds the situation, is time consuming, and inconvenient for the operator. Thus, there is a need for an operator to be able to determine the liquid volume in a tank quickly, and without having to travel to a specific instrument location on the tank and interpret the small dial indicator on the instrument.
The present invention addresses these and other shortcomings of the prior art by providing an apparatus and method that provides light into a translucent storage tank used to store high purity water or chemicals. The light provides a luminous glow in the area of the tank filled with air or other purge gas, with a shadow line being visible at the interface between liquid and air or purge gas. The shadow line is visible by an operator from anywhere in the facility where an unobstructed view to a fill-length vertical section of the tank is visible. Thus, the operator need not be proximate the tank in order to determine the approximate liquid volume in the tank. Moreover, the method and apparatus of the present invention provides a visual indication of liquid volume in the tank while maintaining the purity of the water or chemicals stored therein.